It depends on how you use your machine and the state of it currently - if you have never had malware or viruses, due to running firewall, virus checker, malware checker etc and only visit "mainstream" sites and have multiple backups of your "personal" files, you are unlikely to be any worse off.
If you visit "dubious" sites - porn, warez, torrents etc, you'll probably be paying CrypoLocker before you know it
I will continue to run 3 XP machines as I need to support old software, but I certainly won't be doing any online banking from them.